Gravity or turbulence? - II. Evolving column density probability distribution functions in molecular clouds

It has been recently shown that molecular clouds do not exhibit a unique shape for the column density probability distribution function (N-PDF). Instead, clouds without star formation seem to possess a lognormal distribution, while clouds with active star formation develop a power-law tail at high c...

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Bibliographic Details
Published in:Monthly notices of the Royal Astronomical Society Vol. 416; no. 2; pp. 1436 - 1442
Main Authors: Ballesteros-Paredes, Javier, Vázquez-Semadeni, Enrique, Gazol, Adriana, Hartmann, Lee W., Heitsch, Fabian, Colín, Pedro
Format: Journal Article
Language:English
Published: Oxford, UK Blackwell Publishing Ltd 01.09.2011
Wiley-Blackwell
Oxford University Press
Subjects:
Astronomy
Astrophysics
Earth, ocean, space
Exact sciences and technology
ISM: clouds
ISM: general
ISM: kinematics and dynamics
Numerical analysis
Star & galaxy formation
stars: formation
turbulence
stars: formation
ISM: clouds
ISM: general
turbulence
ISM: kinematics and dynamics
Turbulence
Gravitational contraction
High density
Molecular clouds
Digital simulation
Column density
Log normal distribution
Star formation
Dynamics
Kinematics
Probability density function
Density fluctuation
Power law
Gravity
ISSN:0035-8711, 1365-2966
Online Access:Get full text
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Summary:It has been recently shown that molecular clouds do not exhibit a unique shape for the column density probability distribution function (N-PDF). Instead, clouds without star formation seem to possess a lognormal distribution, while clouds with active star formation develop a power-law tail at high column densities. The lognormal behaviour of the N-PDF has been interpreted in terms of turbulent motions dominating the dynamics of the clouds, while the power-law behaviour occurs when the cloud is dominated by gravity. In the present contribution, we use thermally bi-stable numerical simulations of cloud formation and evolution to show that, indeed, these two regimes can be understood in terms of the formation and evolution of molecular clouds: a very narrow lognormal regime appears when the cloud is being assembled. However, as the global gravitational contraction occurs, the initial density fluctuations are enhanced, resulting, first, in a wider lognormal N-PDF, and later, in a power-law N-PDF. We thus suggest that the observed N-PDF of molecular clouds are a manifestation of their global gravitationally contracting state. We also show that, contrary to recent suggestions, the exact value of the power-law slope is not unique, as it depends on the projection in which the cloud is being observed.
Bibliography:ark:/67375/WNG-SHSRMQ2D-M
istex:19B6AFF062BF20A4E50072921F50089654B8C505
ArticleID:MNR19141
ObjectType-Article-1
SourceType-Scholarly Journals-1
ObjectType-Feature-2
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ISSN:0035-8711
1365-2966
DOI:10.1111/j.1365-2966.2011.19141.x